This invention relates to an acceleration-slippage controller for reducing slippage that occurs between the driven wheel and the road surface during vehicle acceleration.
One example of the prior-art controllers for reducing the acceleration slippage is Japanese Published Unexamined Patent Application S62-67257. When acceleration slippage occurs at a driven wheel, this controller executes both the throttle-valve control and the ignition-timing delay control to reduce the output torque of the engine and slow the revolution of the driven wheel. This device has been contrived because the throttle-valve control and the ignition-timing delay control are individually inadequate because of the respective shortcomings set forth below:
(1) The throttle-valve control cannot quickly lower the output torque of the engine to slow the driven wheel's revolution.
(2) The ignition delay control can alter the engine output torque only to a limited range. When the vehicle is running on a road surface with little friction such as a snow-covered road, it cannot reduce the output torque to less than the critical torque causing the slippage.
When the throttle-valve control and the ignition-timing delay control are started together as in the discussed prior art, each one of them compensates for the other's shortcoming, thus preferably reducing the acceleration slippage by the driven wheel over a wide range of operating conditions.
In the prior-art controller described above, however, the operation of the engine would deteriorate when the two controls are simultaneously executed until the acceleration slippage ends. Although the ignition-timing delay control can reduce the engine output torque quickly, long-term execution of this control raises the exhaust gas temperature, which eventually deteriorates the emission catalyst in the exhaust system. An engine that lowers the exhaust gas temperature by increasing the amount of the fuel supplied to the engine wastes fuel.
The rapid reduction in the engine output torque can also be achieved by the occasional interruption of the fuel supply to each cylinder, instead of by the ignition-timing delay control. Such fuel supply control, however, causes irregular revolution of the engine. The operation of the engine is also adversely affected by such fuel supply omission control.
U.S. Pat. No. 4,721,176 discloses a traction control (acceleration-slippage control) system in which the torque control is used to compensate for a delay in the air flow control. In this prior art, the torque control is executed for a fixed period regarding the delay. Although longer torque control has an adverse effect on the engine conditions such as emission, it is not always appropriate to stop the torque control regardless of the slippage or the slippage control.